Graphing Cosine Functions

Question

I have been practicing graphing cosine functions on IXL pre-Calculus N.10

cos(x-p/4)-1

I am able to under the sinusoidal axis being -1, and also to find the amplitude easily as well.

My trouble stems from the shifting of (x+pi/4). I have watched several videos and something is just not clicking. 

I understand that you shift the function p/4 to the left, but am not quite sure how this is done.

If my x axis is marked: 

-2p   -3p/2   -p   -p/2   0   p/2   p   3p/2    2p 

p/4 is not listed. How do I figure where to start in this case?

Answer 1

Add increments of π/4 to the x-axis.

The shift the graph π/4 to the left.